## To build: ``` make ``` ### Bugs and (Mis)features: The current status of this entry is: > **STATUS: INABIAF - please DO NOT fix** For more detailed information see [2013/mills in bugs.html](../../bugs.html#2013_mills). ## To use: ``` ./mills ``` ## Try: ``` ./mills & ``` While that is running, point your favorite browser at: [http://localhost:8224](http://localhost:8224). ## Judges' remarks: Who will be the first to post an image rendered during a leap-second? ## Author's remarks: ### The Program This program is a handy graphical clock. Simply run the program, click *OK* to any annoying security dialog that pop up (aren't those annoying?), then fire up your web browser and type in the following URL: . You will soon be presented with a lovely dynamically rendered 3D scene that also conveniently tells you the current time! ### Usage Notes The program will continue to give you the time of day as it changes by reloading the page as often as it can render. If you grow tired of watching your life slip by, hit `Control-C` in the original window. Note that if you want to restart the program again, you should wait a minute or two before doing so. For details as to why this is necessary, feel free to Google `"TIME_WAIT"`, `"SO_REUSEADDR"` and `"SO_REUSEPORT"` (with the quotes). And while you are there, click on an ad. They could use the money. It would be possible to fix this by adding ``` n=1,setsockopt(s,SOL_SOCKET,SO_REUSEADDR,&n,sizeof n), ``` at an appropriate spot in the code (an exercise left to the reader). However, as this limitation is documented, it is not technically a bug. ### Details of Operation The program wears many hats (not literally). It is - a web server - a PNG encoder - a ray tracer - a clock It replies to web requests with a PNG image that uses the [Adam7](http://en.wikipedia.org/wiki/Adam7_algorithm) encoding to return data progressively. Since the data is returned in Adam7 format, the scene is displayed initially at a lower resolution and allowed to be progressively refined as time goes on. The ray tracer is integrally tied to the PNG encoder, casting rays in the Adam7 order. The web server uses PNG primarily because of PNG's ability to return data progressively, and not as you might think it being because the PNG standard is so obfuscated as to require both little and big-endian encodings at different spec layers. Since ray-tracing was an obvious choice to return to a web server, I needed something to ray-trace. A static scene would be uninteresting. I took inspiration (as I often do) from the IOCCC remarks file which says ``` At least one judge prefers to maintain the use of the leap-second as part of the world's time standard. ``` Then it was obvious; the code should display the time. It is believed (but not confirmed) that the code will, in fact, display leap seconds correctly. To display the time, of course we would need a font. This font is encoded as a string, using only the C whitespace characters. Clearly, the judges intended this use of whitespace for data compression, since their tool doesn't count whitespace in strings differently than whitespace outside of them. ### User-modifiable Features The code can be user-modified simply by changing the build command line. The following symbols are defined in the [Makefile](%%REPO_URL%%/2013/mills/Makefile): * `-DLT=x1,y1,z1,x2,y2,z2,...` defines the coordinates of the lights in the scene. It should be a comma-separated list of coordinates `(x, y, z)`, three per light. * `-DNL=n` defines the number of lights. It should be equal to the length of the list above (three times the number of lights). * `-DEY=x,y,z` defines the position of the viewer (the eye point) for the scene. The eye is looking at the origin `(0, 0, 0)`. ### Other Build Flags The original program bound the server to `INADDR_ANY` to allow everyone to experience the server's output. The Judges suggested that I instead restrict the bind to `INADDR_LOOPBACK` to reduce security alarms. As a compliant veteran of innumerable post-ship late feature additions, I have modified the [Makefile](%%REPO_URL%%/2013/mills/Makefile) to inject the new code without destroying the beautiful spherical symmetry of the source code. In addition, I have altered the word `sin_port` to the more family-friendly version `win_port` (via `-Dwin_port="sin_addr.s_addr=htonl(2130706433),R.sin_port"`) to protect against curious impressionable youth trying to learn about sockets on the Internet.